Acoustic transducer having diaphragm pivoted in its surround

ABSTRACT

An electronic appliance particularly adapted for converting acoustical energy to electrical energy. The appliance includes a carrier having an elongated piezoelectric element mounted in cantilever fashion on said carrier and a hinged diaphragm mounted on the carrier and connected to the piezoelectric element. The hinged portion of the diaphragm being spaced away from the fixed end of the piezoelectric element. An audio frequency amplification circuit is connected to the piezoelectric element. Components of the circuit are mounted on the carrier and selected components are encapsulated.

United States Patent Carlson et al.

1451 Oct. 31, 1972 ACOUSTIC TRANsDUcER HAVING DIAPHRAGM PIVOTED IN ITS SURROUND Inventors: Elmer Victor Carlson, Prospect Heights; Mead Clifford Klllion, Elk

Grove Village, both of I11.

Industrial Research Products, Inc., Elk Grove Village, 111.

Filed: June 25, 1971 Appl. No.: 157,023

Romans. Application om Continuation of Ser. No. 748,272, July 29, 1968, abandoned. 1

Assignee:

US. (:1. ..'.'179/1s1 R, 179/110 A, 181/32 R Int. Cl ..H04r 7/22, H04r 17/02 Field ofSearch ..179/1 10 A, 181 R, 114 R, 179/115 R; 181/32 R References UNITED STATES PATENTS 2,367,726

Primary Examiner-Kathleen l-l. Claffy Assistant Examiner-Thomas L. Kundert Attorney-Stone, Zummer & Aubel 57] ABSTRACT i An electronic appliance particularly adapted for con-' verting acoustical energy to electrical energy. The appliance includes a carrier having an elongated piezoelectric element mountedin cantilever fashion on said carrier and a hinged diaphragm mounted on the carrier and connected to the piezoelectric element. The hinged portion of the diaphragm being I spaced awayfrom the fixed end of the piezoelectric element 'An audio frequency amplification circuit is connected to the piezoelectric element. Components of the circuit are mounted on the carrier and selected components are encapsulated] I a 2 Chin iprawicsisirs .r A, Q

1/1945 'Lybarger 181/32 microphone for use in a hearing aid the microphone 1 ACOUSTIC TRANSDUCER HAVING DIAPHRAGM PIVOTED IN ITS SURROUND I This application is acontinuationof application, Ser. No. 748,272, filed July..29,' 1968, and now abandoned.

BACKGROUND OF THE INVENTION Electronic appliances which convert acoustic energy to electrical energy have many and varied uses which include applications as microphonesas parts of hearing aids. In order to provide the necessary cosmetic effect in hearing aids, it is particularly desirable to make the components of the hearingaid assmallas possible, including the microphone and associated elements. One of the'types of devices which perform the function of a microphone in a hearing aid includesthe class of miniature transducers which utilize a'piezoelectricelement. Piezoelectric elements forftransducers may take many forms. One form of piezoelectric element is supported at three points and a fourth point, is connectedto an acoustic device for distorting theelement. Another 2 form of piezoelectric element is one which has the element fixed at one end in a cantilever fashion and the free end is fixedto the acoustic device for distorting the piezoelectric element. The acoustic device for distorting the piezoelectric element is a diaphragm. The ordinary construction of a'diaphragm is like apiston, that is, a diaphragm is either supported by a surround which provides for mechanical support for the diaphragm but allows the piston operation of the diaphragm to respond'to a stimulus, or the diaphragm isa formed shape of elastic material designed to deflect at its center when a pressure differential is applied on opposite'sides of its surfaces. The ordinary connection of i the diaphragm to the piezoelectric element has been at the center of the diaphragm. The piezoelectric element has been conventionally located within a cavity behind the diaphragm. I

In the ordinary prior 'art construction of a has been provided as asingle unit and the remainder of the elements which constitute the "audio frequency am- 'plification circuitryhave' been mounted exteriorly .of the microphone. lnutilizing components exteriorly of the transducer element, the various parts were in many instances left open to the atmospheresothat environ-' mental changes often had an effect on the components, thereby affecting the efficiency of the circuit. As aging of insulating of the parts progresses, there has been a change in the operation of the circuit which requires replacement or repair of the parts or a replacement of the entire hearing aid.

Furthermore, it is particularly desirable to maintaina definite mechanical relationship of certain component parts of a hearing aid so that there is a high degree of stability, thereby eliminating any change in electrostatic effect between the parts, such as capacitance which may produce unwanted signals in an audio amplification circuit.

SUMMARY OF THE-INVENTION .60

The present invention relates to an improved electronic appliance and in particular, a miniature microphone, which microphone includes'a construction which allows certain components of electrical .cir- 65 gated piezoelectric element is mounted in a cantilever fashion and has its fixed end on the edge opposite to the edge at which the flapper diaphragm is hinged. The selection of the length of the piezoelectric element and the point of connection of the piezoelectric element with the diaphragm is optimized for efficient operation of the transducer. h

The arrangement of the piezoelectric element beneath the diaphragm permits an apportionment of the elements of the microphone for optimum transfer of energy of the sound wave toan audio amplif cation circuit. The diaphragm, whichhas a contained volume of air on one side thereof, operates as a bellows on the air in the chamber and compression or ratification of thisair operates as a spring upon the diaphragm. The

. the spring of the diaphragm and the piezoelectric element is achieved. It is, therefore, a principal-object of the instant invention to provide an improved miniature microphone which effects optimum transfer of energy from the diaphragm to the piezoelectric element.

' In order-to provide a conservation of space of a he aring aid, the present electronic appliance includes a plurality of .electronic components mounted within a cuitry. Itis another object of thisinvention to provide an electronic appliance in which the space within a transducer housing is utilized for elements of electronic circuitry used in connection with'the piezoelectric element to provide an amplification of the electric signal generated within the piezoelectric element.-

to retard the loss of insulation qualities due to aging.

It is another object of the herein-disclosed invention to provide an improved electronic appliance wherein a transducer and associated circuitry may be conveniently mounted and then easily positioned in a hous- It is still another object of this invention to enclose themost sensitive portions of an audio amplification" circuit entirely within an electrostatic shield to prevent the introduction of noise into the amplification circuit by electric fields;

prevent the introduction of noise into the amplification system as a result of vibration of components, which noise would be created by electrostatic induction.

It is a further object of this invention to provide an improved electronic appliance wherein a portion of an audio amplificationcircuit is mounted immediately adjacent to'a piezoelectric element in order to amplify a signal fromthe elementwithout appreciable impression of noise onto the signal prior to amplification.

transducerhousing and interconnected by printed cir- I Other'objects and uses of the present invention will become readily apparent to those skilled in the art upon a perusal of the following specification in light of the accompanying drawings.

BRIEF DESCRIPTION O TI-IE DRAWINGS FIG. 1 is a plan'view of an electronic appliance embodying the herein-disclosed invention with a portion 1 of a cover broken away in order to showthe construction of a diaphragm; ,1

- FIG. 2 is a cross-sectional side-elevational view taken on Line 2-2 of FIG. 1 showing the interior construction of the electronic appliance shown in FIG. 1;

FIG. 3 is a cross-sectional,end-elevational-view taken on Line 3-3 of FIG. 2 showing the interior construction of the electronic appliance of FIG. 1; I v FIG. 4 is a bottom view. of the electronic appliance shown inFIG. 2, but with the bottom shown partially broken away in order to show the interior construction; and I.

FIG.'5 isa schematic of a circuit diagram of the electronic circuitry for the electronic appliance shown in FIG.1. y

DESCRIPTION OF THE PREFERRED v EMBODIMENT Referring now to the drawings and especially to FIG.

v has an aperture 14 ,contained therein. Mounted on one side of carrier 12 is a diaphragm assembly 16 .and'a converter assembly l8 is mounted onthe other side of the carrier. The carrier is mounted in a housing 20 which has a cover 22 in engagement therewith, and the cover also encloses the diaphragm assembly. The cover 22 includes an aperture 24 which has a bafile plate 26 mounted interiorly of the cover adjacent to the aperture.

The diaphragm assembly includes. a substantially rigid diaphragm-piston28 which is supported by a flexible surround 30. Adhesively fixed to one side of surround 30 is a rigid metal strip 32, which strip prevents the surround from deflecting at the region to which the strip is connected. The remainder of the surround is flexible so that the diaphragm piston 28 when displaced at an-appropriate force pivots about the strip so that a portion of the surround, between the strip and the edge of the piston, acts as a hinge and the diaphragm operates as a flapper diaphragm. It should be noted that any convenient means for making the portion of the surround rigid may be used. It has been found that even a large mass of adhesive may be applied to the portion of the surround to reduce its flexibility and thereby produce a hinge effect. The diaphragm assembly includes re-enforcing rods 34 fixed to the piston and a welt 35 in piston 28 which cooperate to reduce the deflection of the diaphragm piston during normal operation of the pistonl'lhe diaphragmpiston has a drive element aperture 36 positioned closer to its hinged edge than to its free edge.

" The converter assembly 18 includes an elongated piezoelectric element 38 which has one end fixed to the carrier 12' by means of electrically conductive clip 40, which has one end in contact-with the piezoelectric ele ment and the other end is fixed to the carrier. The moving end of the piezoelectric element has a drive element 42 secured thereon, and the'dn've element extends through the aperture 36 and is secured to the diaphragm piston. t

It is important'to note that the overall height of the electronic appliance is determined by the thickness of the housing and cover and the space required by the diaphragm, the carrier, and the piezoelectric element.

The free length of piezoelectric element 38 is entirely however, the deflection would be quite small so there would be very little effect upon piezoelectric element 38. On the other hand, if the piezoelectric element were quite short so that the drive element .42 were connected adjacent to the free end of the "diaphragm piston, there would be a relatively small force available. However, a large deflection would be available,

thereby requiring the short piezoelectric element to.

deflect a substantial amount. The optimum operation is determined by the optimum transfer of energy from the diaphragm to the piezoelectric element-and must be determined individually for each specific piezoelectric element and diaphragm, assembly. In the present preferred embodiment, optimum transfer of energy is achieved when the distance from the hinge connection between the diaphragm and the carrier and the connection between the driveelement and the diaphragm is less than the distance from the fixed end of the piezoelectric element to the connection of the' piezoelectric element to the drive element.

7 In order to utilize the space available in the present electronic appliance, certain electronic components which are used in the circuitry for amplification of a signal from the piezoelectric element are included within the housing. The proximity of the elements to the piezoelectric element allows the weak signal from the piezoelectric. element to be protected by encapsula-.

tion until it is amplified by appropriate component parts so that no appreciable noise or other distortion is added to the signal prior to amplification. Furthermore,

any relative motion between circuit components is prevented so that the likelihood of induction of spurious signalsdue to the incidental mechanical vibrations" and unwanted electrostatic fields in certain electronic components of the amplification circuit is eliminated.

Looking now to FIG. 4, the mechanical connection of various circuit components is shown therein. A fieldeffect transistor 44 is mounted on one side of the carrier proximate the fixed end of the piezoelectric element. A bias impedance element 46 is mounted on the same side of the carrier. with a load impedance element 48. The field-effect transistor includes a gate electrode 50 which is connected to a printed circuit pad 52 on the carrier. The field-effect transistor has a drain electrode 54 which is connected to a printed circuit pad 56 on the carrier which is, in turn, connected to. a lead 58. A third electrode 60 of .the field-effect transistor is a source electrode and is connected to a pad 62. The bias impedance element 46 has one side connected to a printed circuit pad 64 which is connected to the gate electrode and to one side of thepiezoelectric element 38. The other side of the bias impedance element 46 is connected to a printed circuit pad 66, which is connected to a lead 68. One side of the load impedance element 48 is connected to the pad 66 and the other side is connected to pad 62, which pad is connected to a lead 70. The pad 62 extends to a connection with the clip 40 contacting one side of the piezoelectric element 38. The leads 58,68, and 70 are connected to a terminal 72 mounted exteriorly of thehousing. l

- FIG. 5 shows the electrical interconnection of the various parts. ltmay be, appreciated that a batterymay be connected across leads 58 and 68 and a further ampresent device may be easily and economically assembled. Substantially all of the parts may bemounted on the carrier and tested. The carrier with the parts mounted thereon is positioned in the housing and the cover is added to complete the assembly.

' It may be readily appreciated that the instant generatedrby the piezoelectric element. The weak signal from the piezoelectric element is protected and amplified so that extraneous or spuriouselectrostatic fields are not impressedupon the signal prior tov amplification.

Although a specific embodiment of the herein-disclosed invention has been-shown and described in plification stage or receiver may be connected across leads 68 or 58 and 70. For a full description of "the operationof the circuit, reference is hereby made to Patent application entitled Audio Frequency Amplification Circuit, Ser. No. 742,239, having a filing date ofJuly 3,1968.

The components, such as a field-effect transistor 44 and the bias impedance element 46 and an electrode of the piezoelectric element, are encapsulated in a suitable plastic material so that there is no surface leakage between these elements. The clip and the connection of h the piezoelectric element with the other electronic elements is also encapsulated in plastic material 74 so that there is no opportunity for leakage across a surface from the bias impedance element or the field-effect transistor. Also, there is no opportunity for environmental change to have an effect on'the operation of the bias impedance element or the field-effect transistor. It may be readily appreciated since all of these elements are encapsulated and are positioned adjacent to the piezoelectric element, there is little or negligible vibratory effect on these elements. Furthermore, there is little or no electrostatic effect on the relatively weak signal from the piezoelectric element before the signal is amplified in the audio amplification circuit.

From the foregoing description, it is evident that the detail, it isv readily apparent that those skilled in the art may make various modifications and changes in the subject construction without departing from the spirit and scope of the present invention. It is to be expressly understood that the instantinvention is limited only by the appended claims.

We claim: 1

1. An acoustical transducer comprising, in combination, a housing, a carrier, an elongated rigid strip affixed along its length to said carrier, a flexible surround, a diaphragm piston mounted on the surround, said piston having an edge complementary to the rigid strip and adjacent thereto but spaced from the rigid strip by the surround, a portion of said surround being fastened to the elongated, rigid strip, a converter assembly positioned in the housing, and a drive pin connecting said assembly to the piston portion of the diaphragm.

2. An acoustical transducer comprising, in combination, a housing, an elongated rigid strip in the housing, a flexible surround, a diaphragm piston mounted on the surround, said piston having an edge adjacent to said rigid strip but spaced from said rigid strip, a portion of said surround being affixed to said strip, a converter assembly positioned in the housing and a drive pinconnecting said assembly to the piston portion of the diaphragm, whereby said strip defines a linear hinge about which said diaphragm pivots. 

1. An acoustical transducer comprising, in combination, a housing, a carrier, an elongated rigid strip affixed along its length to said carrier, a flexible surround, a diaphragm piston mounted on the surround, said piston having an edge complementary to the rigid strip and adjacent thereto but spaced from the rigid strip by the surround, a portion of said surround being fastened to the elongated, rigid strip, a converter assembly positioned in the housing, and a drive pin connecting said assembly to the piston portion of the diaphragm.
 2. An acoustical transducer comprising, in combination, a housing, an elongated rigid strip in the housing, a flexible surround, a diaphragm piston mounted on the surround, said piston having an edge adjacent to said rigid strip but spaced from said rigid strip, a portion of said surround being affixed to said strip, a converter assembly positioned in the housing and a drive pin connecting said assembly to the piston portion of the diaphragm, whereby said strip defines a linear hinge about which said diaphragm pivots. 